The present invention relates generally to hermetic compressors of the type having a hermetic housing wherein a hermetic terminal is provided for carrying electric current into the housing and, more particularly, to such a terminal having an external enclosure.
Terminal assemblies for hermetic compressors are well known in the art and generally comprise a cup-shaped metallic body member having a plurality of metallic conductor pins extending therethrough. The pins are generally glass sealed to the insulator body to prevent leakage to the atmosphere. A cluster block or female socket arrangement attaches to the hermetic terminal to provide electrical current through the hermetic terminal to the electric motor inside the housing.
A problem associated with electrical terminals for hermetic compressors is that during compressor operation a process known as electrophoresis may occur, whereby metallic particles present within the system migrate toward and deposit upon the hermetic terminal conducting pins and on the surface of the interior glass seal insulator. Also other phenomena may occur in the presence of carbonaceous contaminants within the housing. These particles and contaminants can accumulate to the extent that an electrically conductive path is formed between a pin and the compressor housing, i.e., a ground fault, or between respective pins, i.e., a short circuit, thereby resulting in terminal failure.
Another problem of hermetic terminals is that of service personnel being exposed to hermetic terminals while the terminals are subject to an electric current. This may produce injury in the event of terminal failure. During service, sometimes field technicians remove the terminal enclosure before disconnecting electrical power to the compressor.
Methods for preventing contact with the terminal and protecting against injury in the unlikely event of terminal failure are known and include providing an upwardly extending fence around the hermetic terminal. Such a wall generally comprises a formed piece of metal welded to the exterior wall of the pressure housing thereby leaving an access opening which must then be covered with a combination cover piece and retaining clip. Another protective cover design employs a cover member received on a threaded stud welded to the compressor housing in close proximity to the hermetic terminal and retained thereon by a threaded nut or the like.
A present method for testing the continuity of the internal compressor wiring may result in the protective cover being removed to enable an electrical connection to be made to the compressor terminals. This presents a possible hazard if there is current applied to the compressor when the cover is removed.
It is desired to provide an external terminal shield effective in interrupting electric current during servicing of the compressor and to enable continuity checks to be made with out removing the cover.